This invention relates generally to apparatus and methods for protecting data stored in memory. In one aspect, the present invention more particularly relates to preventing spurious writes to a memory when an operating voltage is applied to or removed from the apparatus, the memory being adapted to store data in response to a control signal from a microprocessor.
Instruments of various types have memories, such as battery-backed solid state integrated circuit devices, in which data are stored under control of a write signal from a microprocessor. Such instruments are powered by electricity which typically can be turned off purposefully, such as for conserving energy, or accidentally, such as due to an outage during a storm. We have noted that when such an instrument is turned on and off, there can be generated spurious signals that adversely affect the memory whereby previously stored data can be lost.
By way of example, there are various types of surface and downhole instruments used in the oil and gas industry as data loggers in that they obtain and store data about characteristics, such as temperature and pressure, relevant to an oil or gas well. At least some modern instruments of this type have microprocessors and memories where the data are stored for later retrieval and use in analyzing the respective wells where the data were gathered. Power to energize these components is typically provided either by batteries or other power sources carried within the instruments or by external sources.
To prevent or reduce data corruption in such instruments during power up or power down electrical transitions, there is the need for an apparatus and method for protecting data stored in a memory, particularly a battery backed memory controlled by a microprocessor subject to being powered up and powered down. More particularly, there is the need in the oil and gas industry for an improved surface or downhole instrument in which existing features and advantages can still be obtained, but without corrupting data stored in memory embedded in the instrument when there is a power application or a power outage.
Although we are aware of a single chip product that purports to control voltage at power up, we are not aware of an apparatus or method which achieves data protection during both power up and power down in the manner of the present invention.